1.Definition and Characteristics of Unshaped Refractories
Indeterminate refractories do not have a complex firing process, the production of raw materials required for easy access, low prices, production process is simple; plasticity is very strong, indeterminate refractory refractoriness and chemical stability can reach the level of similar refractory bricks, easy to prefabricated into a block, easy to generate a variety of complex shapes of products in smelting production, but also for the mechanization of the construction of the furnace; the use of the material is also more convenient, can be directly used or blended for use. The use is also more convenient, can be used directly or deployed after use. However, due to its long time in the low-temperature environment, low strength in the middle temperature, high temperature and long-term use of easy to flake and other shortcomings, so the use of baking technology requires a higher. At the same time, its volume stability is not good enough, high porosity, corrosion resistance is general, the quality may fluctuate, although easy to use, but after use is not very convenient to dismantle, the site must be equipped with special construction equipment.
2.Advantages of indeterminate refractories in the metallurgical industry
As the main refractory material in today’s metallurgical industry, indeterminate refractory material has its own unique application advantages, which are mainly reflected in the following aspects:
Higher refractoriness
The basic property of refractory material is not soften and deformation at high temperature, different refractory material its load softening temperature conditions are not the same, in order to ensure that the thermal equipment in the highest temperature of its structural strength is not destroyed, to maintain a longer service life, we must choose refractoriness higher than the highest temperature of the thermal equipment materials. High-temperature furnace is a commonly used equipment in the metallurgical industry, smelting operations of high-temperature furnace lining refractoriness has high requirements, the refractoriness of non-shaped refractories is generally above 1500 ℃, which can well meet the requirements of the blast furnace working conditions, can extend its service life, but also to enhance the performance of smelting products.
Smaller energy consumption
General shaped refractories need to be processed through a special firing process, which is very complex and consumes a lot of energy, bringing large production costs. The biggest advantage of unshaped refractories is to eliminate the firing process, can avoid a lot of energy waste, in the same working conditions of its energy consumption than the traditional refractory bricks about 15 to 20 times lower on average, can realize a better economy, but also the modern metallurgical industry is widely used in the important reasons.
Higher metallurgical efficiency
Remove the burning link of the non-shape refractory materials, not only can well reduce the consumption of energy resources, but also simplify the smelting process, can greatly save smelting time, improve metallurgical production efficiency. From the point of view of production practice, the use of indefinite refractories is generally 3-5 times higher than the production efficiency of refractory bricks.
Better integrity
Because the volume of indefinite refractories is much smaller than ordinary refractories, it is easier to be transported to meet the conditions of large-volume transshipment, which can reduce the cost of transportation. In addition, indeterminate refractories strong plasticity can be constructed into any shape, and the internal structure is close, strong coagulation performance, the use of indeterminate refractory high-temperature furnace lining is a whole structure, so that in the smelting process is not easy to be damaged by the high temperature, which can greatly make the high-temperature kiln service life, generally can be compared with the traditional refractory bricks to improve the service life by 30%~150%, and because of the reason of the integrality, the sealing performance of the high-temperature furnace is also better than the determinable refractory brick, which can reduce the transportation cost. And because of its integrity, the sealing performance of the high temperature furnace is also much better than qualitative refractory materials, thus reducing energy consumption on the whole.
3.Specific application
1、 The application of non-conformable refractories on the blast furnace
As an important equipment in the metallurgical industry, the traditional blast furnace is made of steel plate as the shell, and refractory brick lining is built inside the shell, which is generally made of high alumina cement and phosphoric acid high alumina refractory castables prefabricated blocks for hoisting and masonry, and the modern blast furnace is mainly made of resin-bonded aluminum-carbon unburnable bricks. Water-cooled wall of large blast furnace using SiC castables, furnace bottom bedding and peripheral brick joints using silicon nitride materials to fill, the use of castable refractories for furnace walls has become a common feature of the industry can achieve better results, such as Japan’s Fukuyama Steel Pipe Plant No. 2 blast furnace on the use of Al₂O₃ material for six consecutive years have not seen large areas of spalling phenomenon. At present, Al₂O₃-SiC-C (ASC) and mullite SiC-C are the commonly used non-shaped refractories on the blast furnace trench at home and abroad. Japan’s blast furnace is mostly used “ASC” castables, Western industrial powers generally SiC-C battered materials, our domestic metallurgical industry to SiC steel jade-based.
2、 The application of indefinite refractory materials on the ladle
Refractories for ladle are gradually being replaced by indeterminate refractories as a result of the increase in the steel discharge temperature and the increase in the retention time of liquid steel in the ladle. Based on the indeterminate characteristics of ladle, production automation can be realized, which helps to improve capacity and production efficiency. Practical experience shows that the indeterminate shape of the ladle side wall can save about 40% of the maintenance labor hours; when the ladle is completely indeterminate, the labor-saving effect can reach 70% and above. At present, many iron and steel enterprises of the ladle are used Al₂O₃-spinel castables as refractory materials, this material has a better corrosion resistance, high temperature structural impact is small, can extend the service life of thermal equipment long. However, its use performance will still be affected by the steel temperature and steel residence time, in order to solve this technical problem, has given birth to the Japanese research and development of Al₂O₃-MgO castables, aluminum-magnesium carbonaceous refractory castables and magnesium refractory materials, the strength and permeability resistance of these new materials have been greatly improved, and the use of the effect is also better in the steel ladle.
3、 Application of irregular refractory materials on heating furnace
The heating furnace is used to heat the billet at high temperature, because the maximum temperature is up to about 1400℃, its roof and lining can be constructed by using castables or plasticizable materials. Generally, the lining of large-scale step-type heating furnace can be made of plasticized refractory material, and the average service life can reach about 12-15 years, while the step-type heating furnace of high-speed wire rod workshop, due to the larger furnace body and higher refractoriness requirements, can be made of clay structural castables, which is not only convenient for mechanical construction, but also has no honeycomb after demolding and good mobility, and it can meet the operating environment requirements of thermal equipment very well. The material is not only convenient for mechanical construction, but also has no honeycomb after demolding and good fluidity, which can well meet the requirements of thermal equipment.
4.Growing trend
1.Material development direction
First of all, the past indefinite refractory products are mainly selected neutral, acidic oxides and other materials, made of indefinite refractory heat-resistant and corrosion-resistant performance has been unable to meet the higher requirements of the metallurgical process, and alkaline oxide materials, oxides and non-oxidized composite materials based indefinite refractories can be a good solution to the problem, which is the current metallurgy with indefinite refractories of a This is also one of the current metallurgical indefinite refractories development trend.
At present, unshaped refractories are also gradually developed from a single refractory castables to refractory compression castables, and in the traditional types of plastic, pounding materials, projectile materials, such as the emergence of castables, spraying filler materials and other new materials. Such as high-quality lightweight aggregate, refractory powder, binding agent, additives formulated from lightweight castables, with lower thermal conductivity, stronger thermal insulation, better thermal shock resistance, can be widely used in industrial furnaces and thermal equipment insulation parts. The continuous research and development of refractory materials further improves the efficiency of metallurgical operations and industrial economy.
2.Combined approach development direction
First of all, the bonding method of indefinite refractories in metallurgical industry has experienced the development from water and bonding, chemical bonding, water and bonding + cohesive bonding, to polymerization bonding, and towards the direction of cohesive aggregation, which follows the development route of high impurity-low impurity-no impurity, and the purity of the bonding agent is getting higher and higher [6]. Secondly, in recent years, with the progress of blast furnace technology, the performance of indefinite refractories also put forward higher technical requirements, in order to reduce the damage of the blast furnace and improve the metallurgical efficiency, the combination of indefinite refractories also began to shift from high water, low water to no water, and gradually to the direction of high-density development, to further improve the overall performance of the indefinite refractories in the metallurgical industry.
Indefinite refractories have special advantages that fixed refractories do not have, and they are an important support for the high-quality development of the modern metallurgical industry, although there are still certain defects, but their overall development is on the rise. With the continuous progress and improvement of technology, the new type of indefinite refractories through the development of innovation, it will certainly promote the deepening development of the entire metallurgical industry.